The present invention relates, in general, to a method of friction or inertia welding and, in particular, to a method of friction welding wherein the interface surfaces between two solid metal components to be friction welded are uniquely shaped.
Friction welding is a well known process wherein two or more metal or plastic components can be joined together by using heat generated by friction as the components are rubbed against each other to produce a welded joint. In friction welding, two metal components to be joined together are moved either relatively rotationally or reciprocally with respect to one another and, simultaneously, are pressed against each other until sufficient heat is generated by friction between the components to produce the friction welded joint.
Generally, the relatively moving surfaces of the components at which the friction welded joint is to be produced are matched in shape with one another. In most cases, such surfaces are planar and parallel to one another. However, in some instances, it is desirable to shape the interface surfaces of the components to be joined to control the initial contact between the interface surfaces such that the frictional heat produced is initially concentrated at certain areas of the interface surfaces. For example, in U.S. Pat. No. 3,762,030, the interface surface of a first metal component to be joined to a second metal component is provided with a depression so that the initial contact between the interface surfaces will be at the peripheral areas of such surfaces. It has been found that such a configuration is desirable when welding one component having hot strength properties greater than that of a second component.
In other friction welding methods, the interface surfaces of one of the components is provided with a convex-shaped interface surface such that initial contact occurs and frictional heat builds up at the central contact area. For example, in friction welding a forged yoke component to an associated bar stock of a predetermined length to produce a vehicle axle shaft assembly, it has been found desirable to shape the interface surface of the yoke in a conical-shaped configuration having a relatively small radial draft. However, it is difficult to produce such a conical-shaped surface during the forging operation of the yoke since, due to the inherent die shift during the forging operation, the apex on the conical-shaped interface surface produced by the forging is not always located at the center of the interface surface. Thus, in order to produce a proper weld joint without any cold spots located in the central area, it has been found that the conical-shaped interface surface of the yoke forging should be qualified by a separate machine operation prior to the friction welding operation.